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Biology - Animals Invertebrates

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    Study Guide Biology – Animals: Invertebrates 1. Cnidaria Cnidaria is a group of animals that includes hydras, jellyfish, sea corals, and sea anemones . Most cnidarians live in marine (ocean) environments , although a few can be found in freshwater. 1.1 Body Structure and Symmetry Cnidarians have a tissue - level organization , which means their bodies are made of tissues but not complex organs. Their body plan shows radial symmetry . This means their bodies are arranged in a circular way, with body parts spreading outward from the center — like the spokes of a wheel. 1.2 Tentacles and Stinging Cells Around the body opening, cnidarians have tentacles . These tentacles contain special stinging cells called cnidocytes . Cnidocytes help the animal: • Defend itself from predators • Capture food , such as small animals in the water When triggered, these stinging cells release toxins that immobilize prey. 1.3 Digestion and the Gastrovascular Cavity Cnidarians digest food inside a central space called the gastrovascular cavity . This cavity has two main roles: • It helps with digestion • It also helps distribute nutrients throughout the body Cells lining the cavity release digestive enzymes that break food down. The digested nutrients are then absorbed directly into the cells.

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    Study Guide 1.4 Simple Nervous System Instead of a brain, cnidarians have a loose network of nerve cells spread throughout their tissues. This network helps coordinate basic activities like movement and feeding. 1.5 Two Main Body Forms Cnidarians have two basic body shapes : • Polyp : ○ Shaped like a hollow vase ○ Usually attached to a surface ○ Example: Hydra • Medusa (plural: medusae ): ○ Shaped like an upside - down umbrella ○ Free - swimming ○ Example: Jellyfish Both forms have a three - layered body wall that makes up their outer surface. 2. Quiz Cnidaria 1. Question Fill in the blank: What type of body symmetry do cnidarians exhibit? Answer Choices • bilateral • radial • none

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    Study Guide Correct Answer radial Why This Is Correct Cnidarians have radial symmetry , which means their body parts are arranged around a central axis. They can be divided into similar halves in many different directions, like the spokes of a wheel. This type of symmetry is common in animals such as jellyfish and sea anemones, allowing them to interact with their environment from all sides equally. 2. Question Fill in the blank: Which of the following do cnidoblasts NOT contribute to? Answer Choices • defense • feeding • reproduction Correct Answer reproduction Why This Is Correct Cnidoblasts (also called cnidocytes) are specialized stinging cells found in cnidarians. They help the animal defend itself and capture prey for feeding by releasing toxins through stinging structures. However, cnidoblasts have no role in reproduction . Reproduction in cnidarians occurs through processes like budding or the production of gametes, not through stinging cells. 3. Question Fill in the blank: Where does digestion occur in a cnidarian?

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    Study Guide Answer Choices • amoebocytes • gastrovascular cavity • stomach Correct Answer gastrovascular cavity Why This Is Correct In cnidarians, digestion takes place in the gastrovascular cavity , which is the central body cavity. Cells lining this cavity release digestive enzymes that break down food, and the digested nutrients are then absorbed by the cells. Cnidarians do not have specialized organs like a stomach, and amoebocytes are not involved in digestion in these animals. 3 . Platyhelminthes Platyhelminthes are commonly known as flatworms . Examples include planarians , flukes , and tapeworms . As their name suggests, these animals have flat bodies, which helps them exchange gases and nutrients easily through their body surface. 3 .1 Body Symmetry and Head Development Flatworms show bilateral symmetry . This means the left and right sides of their bodies are mirror images of each other. Bilateral symmetry allows for better movement in one direction. Another important feature is cephalization . This means that one end of the body acts like a head. The head region contains: • A cluster of nerve cells that works like a simple brain • Special areas that can sense light, chemicals, and touch (pressure) This makes flatworms more responsive to their environment compared to simpler animals.

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    Study Guide 3 .2 Tissue Layers and Organ Systems Flatworms have three distinct layers of tissue , and all of these layers are made of living cells. Because of this, they have true organs and organ systems . These systems help with: • Digestion • Movement • Excretion • Reproduction This level of organization is more advanced than what we see in earlier animal groups. 3 .3 Digestive and Excretory Systems The digestive system of a flatworm is a muscular tube with only one opening . This opening acts as both the mouth and the exit for undigested food. The excretory system helps remove excess water and waste. It is made of: • A network of tiny water - collecting tubules • These tubules empty into sacs that release waste to the outside of the body 3 .4 Movement and Nervous Control Flatworms move using muscle cells located just below the epidermis (outer body layer). These muscles contract and relax to produce movement. The process is carefully controlled by signals from the nervous system , allowing smooth and directed motion. 3 .5 Reproduction Most flatworms are hermaphrodites , meaning each individual has both testes and ovaries . During reproduction: • Two flatworms pair up • They exchange sperm and eggs

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    Study Guide • Fertilization occurs after this exchange This increases the chances of successful reproduction. 4 . Quiz Platyhelminthes 1. Question Fill in the blank: Which of the following is NOT a member of Platyhelminthes? Answer Choices • flatworm • leech • tapeworm Correct Answer leech Why This Is Correct Platyhelminthes are flatworms , which include organisms like flatworms and tapeworms . They have flat, soft bodies and simple organ systems. A leech , however, belongs to a different group called Annelida (segmented worms), not Platyhelminthes. 2. Question Fill in the blank: What trait is possessed by Platyhelminthes, but NOT by Cnidaria? Answer Choices • a body cavity • cephalization • radial symmetry

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    Study Guide Correct Answer cephalization Why This Is Correct Cephalization is the concentration of nerve tissue and sensory organs at one end of the body, forming a head region. Platyhelminthes show cephalization, which helps them move in a directed way and respond more effectively to their environment. Cnidarians do not have cephalization. Instead, they have a simple nerve net and radial symmetry , with no distinct head or tail. 3. Question Fill in the blank: Which of the following statements about Platyhelminthes is FALSE ? Answer Choices • Most have both testes and ovaries. • They have true organs. • They lack organ systems. Correct Answer They lack organ systems. Why This Is Correct Platyhelminthes (flatworms) have true organs and simple organ systems , such as a digestive system and an excretory system. Therefore, saying they lack organ systems is incorrect. The other statements are true: • Most platyhelminthes are hermaphroditic , meaning they have both testes and ovaries. • They show organ - level organization , which is more advanced than tissue - level organization.

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    Study Guide 5 . Annelida Annelida is the phylum that includes segmented worms . This group includes worms that live in mud and sand , familiar earthworms , and leeches . Even though they may look simple, annelids have a surprisingly well - organized body structure. 5 .1 Key Body Features All segmented worms share several important characteristics: • Bilateral symmetry – the left and right sides of the body are mirror images • Cephalization – the front end of the body is more developed and acts like a head • An open digestive system – food enters through a mouth and waste exits through an anus • Segmentation – the body is divided into repeating sections • A body cavity – space inside the body that holds organs These features allow annelids to move efficiently and carry out complex body functions. 5 .2 The Coelom: A True Body Cavity Annelids have a true body cavity , called a coelom . This is a fluid - filled space located between the innermost tissue layer and the outer two layers. The coelom is important because: • It provides space for digestive and reproductive organs to become more complex • It cushions the organs, allowing them to move and function independently of the body wall • Digestive activities can happen smoothly without interfering with other body tissues 5 .3 Segmentation and Excretion The bodies of earthworms and other annelids are made up of many repeated segments . These segments are separated internally by partitions, giving each section some independence. Most segments contain nephridia , which are funnel - shaped excretory structures . Nephridia:

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    Study Guide • Remove excess water and waste from the body • Reabsorb needed water • Release waste to the outside through tiny pores in the skin 5 .4 Movement and the Hydrostatic Skeleton Each body segment has two types of muscles: • Circular muscles • Longitudinal muscles When these muscles contract, they push against the fluid in the coelom. This creates a hydrostatic skeleton , a water - based support system that helps the worm: • Maintain its shape • Move efficiently through soil or water 5 .5 Digestive and Circulatory Systems Annelids have a digestive system that runs the entire length of the body, allowing food to be processed step by step. They also have a closed circulatory system , meaning blood stays within blood vessels. Blood is moved through the body by the contraction of several muscular vessels called hearts , which pump blood efficiently to all body segments. 5 .6 Reproduction All annelids reproduce sexually . This method of reproduction helps increase genetic variation within the species. 6 . Quiz Annelida 1. Question Fill in the blank: An annelid’s body cavity is:

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    Study Guide Answer Choices • coelom • nonexistent • pseudocoelom Correct Answer coelom Why This Is Correct Annelids (such as earthworms and leeches) have a true body cavity called a coelom . This cavity is completely lined with mesoderm and allows space for internal organs to develop and function efficiently. A nonexistent body cavity is seen in flatworms, and a pseudocoelom is found in organisms like roundworms — not annelids. 2. Question Fill in the blank: Which of the following is NOT a benefit of having a true body cavity? Answer Choices • cushioned digestive system • more complex reproductive and digestive organs • the ability to grow larger organs Correct Answer cushioned digestive system Why This Is Correct A true body cavity (coelom) mainly allows organs to develop independently , become more complex , and grow larger without interfering with one another. These features support advanced organ systems and greater body size.

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